Problem: How many significant figures does $00.0645100$ have?
Explanation: Identify the non-zero digits and any zeros between them. These are all significant. $00.0{6451}00$ Leading zeros are not significant. $\color{orange}{00.0}{6451}00$ Since there is a decimal, trailing zeros are significant. $\color{orange}{00.0}{645100}$ Counting all the significant digits gives us 6.